Linear generator

ABSTRACT

A linear generator according to the present invention is adapted to generate a voltage proportional to the speed of a movable member or rotor and enable the movable member to be smoothly moved. The linear generator includes a first part having permanent magnets fixed to a yoke which are magnetized to the direction perpendicular to the longitudinal direction of a shaft, and a second part having a coil wound around the bobbins and a housing enclosing the coil. A plurality of magnetic poles are provided between the magnets and coils.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear generator adapted to generatea voltage proportional to the speed of a movable member or rotor andenable the movable member to be smoothly moved.

2. Statement of Prior Art

As disclosed in U.S. Pat. No. 4,500,827, a linear generator according toa prior art is constituted in such a way that a yoke and permanentmagnets are fixedly mounted to a reciprocating shaft to provide amovable member or rotor, and magnetic poles, bobbins and coils aredisposed oppositely to said permanent magnets to provide a stator. Inthis instance, the length of one permanent magnet is selected to becomehalf of the stroke of a shaft, and the respective magnets are spaced bythe distance corresponding to the stroke of the shaft and juxtaposedwith different polarities. The width of the magnetic poles and the coilsis made equivalent to that of the permanent magnets.

The magnetic resistance in relation to a permanent magnet is thesmallest one when the permanent magnet is displaced to the positionopposite or facing the magnetic pole and the largest one when thepermanent magnet is displaced to the position opposite or facing to thecoil. Accordingly, as explained above, the arrangement of the permanentmagnet, the magnetic pole and the coil according to a prior art causesthe magnetic resistance to vary remarkably depending on the displacementof the permanent magnet and also causes the magnetic energy being storedin the air gap defined between the permanent magnet and the magneticpole to vary so considerably that a big cogging force will be generated.The term "cogging force" is used herein to express thrust at the time ofunloading. Consequently, the peak of the force for driving the movablemember or rotor is so high that a driving source for high thrust will benecessitated.

The present invention has therefore as the subject to solve to eliminatethe drawbacks caused by the prior art as above explained.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems in the prior art, thepresent invention provides a linear generator comprising a first partwhich has a yoke fixed to a shaft and a plurality of permanent magnetssubstantially contacting to the longitudinal direction of said shaft andfixed to the surface of said yoke and in which said permanent magnetsare magnetized to the direction perpendicular to the longitudinaldirection of said shaft and each of adjacent permanent magnets has apolarity opposite to each other; and a second part which has a pluralityof magnetic poles facing oppositely to said permanent magnets withclearance therebetween, coils wound around the bobbins made ofnon-magnetic material and a housing enclosing said coils, wherein saidplurality of magnetic poles being provided between said permanent magnetand said coils.

The magnetic path of the magnetic flux generated by the permanentmagnets is varied depending on the relative displacement of the firstpart and the second part and the amount of the magnetic flux interlinkedrelative to the coils is also varied, thereby resulting in voltage onthe coils. And voltage proportional to the relative displacementvelocity or speed of the first part and second part is obtained, so thatwhen the generator is driven in the speed having a sinusoidal shape,excellent alternate current output without any deformation may beobtained. It is also to be noted that the movable member may be operatedsmoothly and the maximum thrust at the driving source may, becomesmaller. The acompanying drawings illustrate the embodiment of theinvention and together with the description serve to explain theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the sectional view showing an embodiment of the presentinvention,

FIG. 2 is the side elevation of the movable member,

FIG. 3 is the sectional view showing another embodiment of the presentinvention, and

FIG. 4 is the partial sectional view showing the relative dimensions ofthe respective components.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Firstly, reference is made to FIG. 1 wherein the shaft 1 connected tothe reciprocating rod of a stirling engine not shown is supported by theholder 3 through bearings 2. The shaft 1, the bearings 2 and the holder3 are made of non-magnetic bodies. A plurality of permanent magnets 5are juxaposed to the shaft 1 through the yoke 4 made of magneticmaterial. Said shaft 1, said yoke 4 and said permanent magnets 5constitute the movable member 6. The length of each one permanent magnet5 is selected to be equal to the stroke 7 of linear reciprocation of themovable member 6 and the permanent magnets are arranged in a manner totightly contact with each other and the polarity of each adjacentpermanent magnet is opposite to each other.

A plurality of magnetic poles 8 are so disposed that they are spacedfrom but facing opposedly to said permanent magnets. The number of themagnetic poles 8 is more than that of the permanent magnets 5 by one.And the overall length of the permanent magnet 5 is shorter by thereciprocation stroke of the movable member 6 than the overall length ofthe magnetic poles 8. The small clearances defined between each magneticpole 8 will be located substantially at central position of eachpermanent magnet 5 when the generator is at the neutral position and theopposite ends of each permanent magnet 5 is located substantially at thecentral position of each magnetic pole 8. The length of each magneticpole 8 is selected to be 80% to 95% of that of each permanent magnet.Consequently, while the movable member 6 is reciprocating, the permanentmagnets 5 are moved always oppositely facing to the magnetic poles 8, sothat the magnetic resistance between the permanent magnets 5 and themagnetic poles 8 is kept constant and variation of the magnetic energystored in the air gap is also so small that cogging force is likewisesmall.

Coils 10 are disposed outwardly of the magnetic poles 8 through bobbins9. Said coils 10 are arranged opposedly to said permanent magnets 5 andyokes 11 are arranged in between the coils. A housing 12 is providedoutside of said yokes 11 to define the outer configuration of thegenerator together with the holders 3. The magnetic poles 8, the yokes11, the coils 10 and the housing 12 constitutes the stator 13. It is tobe noted that the stator 13 is made of magnetic material except thebobbins 9.

In FIG. 3, there is shown another embodiment of the present invention.In the embodiment as shown in FIG. 3, the constitution is identical tothat of FIG. 1 except that the overall length of the permanent magnets 5is made longer than the overall length of the magnetic poles 8 by thestroke 7 of reciprocation of the movable member 6 and there is such acase as a permanent magnet 5 will not face oppositely to a magnetic pole8 while the movable member 6 is reciprocating. As such, the explanationof the constitution of said embodiment will not be repeated here.According to this embodiment, since there are such cases as a permanentmagnet 5 will not face oppositely to a magnetic pole 8 during operationof the generator, and the magnetic resistance will vary, so that themagnetic energy will also vary and cogging force will be generated. Thiscogging force has such a tendency as to be concentrated toward thecenter of the shaft 1 and exhibits the same characteristics as a spring.Therefore, the embodiment shown in FIG. 3 makes use of the spring effectand performs two functions, that is, power generation and spring effect.

As it is clear from disclosure of the embodiments as above explained,the linear generator according to the present invention is characterizedin such a constitution as "(1) The permanent magnets 5 are disposed witheach adjacent permanent magnet having an opposite polarity. (2) Thewidth `L` of the magnetic pole opposedly facing to the permanent magnetis made as wide as possible as shown in FIG. 4." In this instance, whenthe permanent magnets 5 as the movable member come to the positionfacing opposedly to the magnetic poles 8, the magnetic flux φ generatedby the permanent magnets is divided into the composition φ₁ interlinkedon the coils 10 and the composition φ₂ flowing directly to the adjacentmagnetic poles. Since the magnetic flux which can be effectively usedfor generation is the composition φ₁ and the composition φ₂ will causemagnetic saturation of the iron core, generate useless thrust for themovable member and so forth, it is necessary to keep the magnetic forceat a low level. When the width `L` of the magnetic poles 8 is toowidened, φ₂ will be increased due to reduction of the magneticresistance between said width ` W`. And if the width W becomes null,majority of the flux φ will become φ₂, so that the performance of thegenerator will become poor. If the width `L` will be shortened so as torestrict generation of φ₂, then the characteristic (2) as abovementioned will be contradicted and the undesirable cogging force will beincreased. In view of this, if the performance of the generator is setwith φ₂ /φ₁ ≦0.4, then W/L will be 0.05-0.20 or preferably 0.1-0.15. Inthis preferable range, the cogging force may be kept less than 10% ofthe looding thrust. On the other hand, if W/L is 0.3, then the coggingforce will increase to the order of 50%. Therefore W/L should be keptless than 0.20.

According to the present invention, voltage proportional to the velocityof the movable member will be obtained, so that the generator may beused also as a speed sensor. Furthermore, since magnets may be disposedentirely on the surface of the movable member, the output per unitvolume and mass may be increased.

It will be apparent to those skilled in the art that variousmodifications can be made within the scope of the appended claims andtheir equivalents.

What is claimed is:
 1. A linear generator comprising a first part whichhas a yoke fixed to a shaft and a plurality of permanent magnetssubstantially positioned along the longitudinal direction of said shaftand fixed to the surface of said yoke and in which said permanentmagnets are magnetized in the direction perpendicular to thelongitudinal direction of said shaft and each of adjacent permanentmagnets has a polarity opposite to each other; and a second part whichhas a plurality of magnetic poles facing oppositely to said permanentmagnets with clearance between said poles and said permanent magnets andsaid poles are spaced from each other by a specified distancetherebetween, coils wound around bobbins made of non-magnetic materialand a housing enclosing said coils, wherein said plurality of magneticpoles are provided between said permanent magnet and said coils.
 2. Alinear generator as claimed in claim 1, wherein the longitudinal lengthof each magnetic pole is shorter than that of each permanent magnet bysaid clearance between said magnetic poles.
 3. A linear generator asclaimed in claim 1, wherein the area of the opposed surface of saidmagnetic poles to said permanent magnet is substantially constant inaccordance with reciprocation of first part and second part.
 4. A lineargenerator as claimed in claim 1, wherein said clearance between saidmagnetic poles is opposed to said coils.
 5. A linear generator asclaimed in claim 1, wherein the number of the permanent magnets is lessthan that of the magnetic poles, and the overall length of the permanentmagnets is shorter than that of the magnetic poles by the stroke ofreciprocation of one part relative to the other part, so that thepermanent magnets are always facing oppositely to the magnetic poles. 6.A linear generator as claimed in claim 1, wherein the number ofpermanent magnets is more than that of the magnetic poles and theoverall length of the permanent magnet is longer than the overall lengthof the magnetic poles at least by the stroke of reciprocation of onepart relative to the other part, so that a part of the permanent magnetswill not face oppositely to the magnetic poles.
 7. A linear generator asclaimed in claim 3, wherein said shaft is connected to the rod fixed tothe piston of a stirling engine.
 8. A linear generator as claimed inclaim 4, wherein the respective clearance between said spaced magneticpoles is located opposedly facing substantially to the central portionof the respective permanent magnets when the generator is in a neutralposition.
 9. A linear generator as claimed in claim 1, wherein saidshaft is reciprocated with a substantially constant stroke, said firstpart constitutes the movable member and said second part constitutes thestator.
 10. A linear generator as claimed in claim 1, wherein the ratioof the distance spacing the respective magnetic poles in thelongitudinal direction to the width of the surface of the respectivemagnetic poles facing oppositely to the permanent magnets is 0.05 to0.2.
 11. A linear generator comprising a first part which has a yokefixed to a shaft and a plurality of permanent magnets fixed to the outersurface of said yoke and in which said permanent magnets are magnetizedin the direction perpendicular to the longitudinal direction of saidshaft and each of adjacent permanent magnets has a polarity opposite toeach other; and a second part which has a plurality of magnetic polesfacing oppositely to said permanent magnets with clearance between saidpoles and said permanent magnets and said poles are spaced from eachother by a specified distance therebetween, coils located outside ofsaid magnetic poles and wound around the bobbins made of non-magneticmaterial and a housing enclosing said coils, wherein at least one ofsaid first and second parts has a means for minimizing the change ofopposed area of said magnetic poles and said permanent magnets.